Beach Closures: Cyanobacteria and Phosphorus in New York’s Lakes

Cyanobacteria blooms have closed beaches regularly this summer across New York State. While it may feel like a nuisance to not be able to cool off at your local beach, these blooms force swimming areas to close because they can be dangerous. To protect yourself, your loved ones, and pets, it is important that you understand how to recognize them and what you should do if a bloom is present at a beach you visit.

Cyanobacteria, also known as blue-green algae, are bacteria that use sunlight for growth. They can form dense clusters, called blooms, in warm, nutrient-rich waters. They can sometimes contain toxins. These toxins can irritate skin and cause symptoms of hay fever to those exposed to them by touching or inhaling them. If ingested, the toxins can affect nervous system functioning and have been known to kill dogs. As a result, they are sometimes called harmful algae blooms or HABs.

Cyanobacteria blooms have naturally occurred for decades, but they continue to become more frequent, especially in shallow areas lakes. Their presence leads to local beach closures. This is especially true during summer, but they have also been observed at other times of the year.

Unfortunately, because they flourish on warm, calm days, cyanobacteria blooms are disproportionately present on the days people look to lakes for solace from the extreme heat.

How to recognize a cyanobacteria bloom

Cyanobacteria blooms can look foamy or like pea soup or spilled paint. They can also form streaks in the water. They are generally green to blue-green in color, but they can also be red, brown, or white. They can form scums, clumps or floating mats that can accumulate on shore and give off a foul smell.

From Memorial Day to Labor Day, many swimming areas in New York State are monitored regularly for cyanobacteria. At monitored locations, once a bloom is confirmed, staff post the swimming area as closed. How a beach is marked can vary beach to beach, so be sure to check with attendants at beach entrances (when available), or check beach websites ahead of your visit, and look for signs along the beach, at the entrance or on other buildings or structures at the beach.

Swimming area closures at state park beaches in New York and Vermont are posted on relevant state websites including this New York Department of Environmental Conservation (DEC) website and this Vermont DEC website.

If cyanobacteria are present at one beach, that does not mean all beaches on a given lake are closed. Blooms are influenced by such things as wind direction, water depth, and currents, so different beaches can have very different conditions; some may be experiencing blooms, while others not far along the shoreline may not be. It’s important to check the status of the specific beach you plan to go to beforehand so that you can change your plan if it is closed.

Cyanobacteria can be dangerous to humans, pets, and other wildlife. While not all cyanobacteria blooms are toxic, there is no way of knowing whether toxins are present in a cyanobacteria bloom at any given time.

As cyanobacteria blooms – and any toxins they may harbor – can come and go within a short time, it’s advisable to visually inspect any beach you visit before swimming or recreating in another way in or on the water.

If you see something that you suspect may be a cyanobacteria bloom — whether or not the beach is posted as closed — it’s best to stay out of the water and to keep your pets and children out as well. Even splashing in shallow water or walking in the water can be dangerous as that could expose you to toxins in the air above a bloom.

There are various toxins that can be present in cyanobacteria that have different impacts on health with effects ranging from liver to nerves, to skin. These toxins can be especially harmful to dogs as they are more likely to drink the water and can be attracted to the bloom odors.

Researchers do not know the extent of impacts cyanobacteria exposure can have to humans or animals, especially through airborne pathways. So, if you are in doubt if a bloom is cyanobacteria, it’s best to stay out.

What causes blooms

Warming waters, nutrient runoff, and more intense rainstorms are contributing factors behind the increasing frequency of cyanobacteria blooms and subsequent beach swimming area closures. For example, the recent extreme storm events are estimated to have brought as much phosphorus into Lake Champlain as was transported to the lake via streams and rivers in all of 2022. Another driver amplifying these issues is something called legacy phosphorus.

Legacy phosphorus is the accumulated phosphorus in lake sediments. It came from decades of historical phosphorus inputs that flowed into lakes from streams and rivers. What is now legacy phosphorus in the lake bottom originated on the land in areas both near and far from the lake in question. It moved across the landscape in runoff little by little each year, settling to the bottom over time.

Since phosphorus moves attached to soil particles, a lot of phosphorus has entered lakes in spring snowmelt runoff when a lot of bare ground is available to wash away with snowmelt. In addition, a significant amount of phosphorus has reached lakes when traveling in runoff following major rainstorms like we saw in early July this year.

Once phosphorus has accumulated in the lake bottom, it is regularly released back into the water column, feeding cyanobacteria bloom growth — even without any new external inputs of phosphorus from the landscape.

However, it is still important for us to take action to limit the amount of phosphorus that reaches lakes and adds to the legacy phosphorus. Every individual who owns or manages land can take steps to limit the amount of nutrients that runoff from their land.

As a resident, some simple ways to reduce phosphorus runoff include:

• Installing rain gardens or rain barrels. These help slow the flow of stormwater runoff and allow that water to sink into the ground where it can be filtered and nutrients like phosphorus can be held in the soil.
• Clearing leaves and other debris from storm drains. Clogged storm drains mean stormwater flows over streets and other impervious surfaces longer, collecting more pollutants. Since leaves also contain phosphorus, they exacerbate the amount of phosphorus entering lakes.
• Getting a soil test before using fertilizer that contains phosphorus. In both New York and Vermont, it is illegal to use phosphorus fertilizer unless a soil test necessitates it. Many soils in New York State have plenty of phosphorus in them to grow a bountiful lawn.
• Volunteering with a local watershed organization that is taking steps to prevent erosion (and therefore phosphorus transport) from lakeshores or streambanks by planting native trees and shrubs.

Learn more about what you can do in this storymap focused on residential stormwater. The more each individual can do to prevent stormwater runoff from leaving their own property, the less phosphorus will reach our lakes.

Photos, from above: Various cyanobacteria blooms in New York State (including last photo); and side by side images of the Burlington, VT waterfront without a cyanobacteria bloom (left) and with a severe cyanobacteria bloom (right) that formed within a day. See DECE’s gallery of cyanobacteria blooms here.